Wire electrodes for the spark erosion process are produced, as a rule, with a high-strength core which, moreover, should also be a good electric conductor. Cores made from brass or composite cores, in which a steel nucleus is surrounded by a copper or brass layer, have proved appropriate for producing high strength. To increase the cutting capacity of wire electrodes of this type, a sheath layer, whic[0088] consists, as a rule, of zinc or a zinc alloy, is coated onto these. Very good cutting capacities have been achieved with wire electrodes provided with a pure zinc coating. However, the cutting capacity of these electrodes decreases when tall workpieces are to be cut. The reason for this is that the pure zinc of the sheath layer evaporates rapidly and is therefore consumed in a very short time, so that the wire electrode then cuts with its core material, thus again reducing the cutting capacity as a whole.
Tests have shown that, where tall workpieces are concerned, better cutting capacities are achieved when the zinc of the sheath layer is a constituent of an alloy. It has proved advantageous, here, to produce the sheath layer from a homogeneous beta brass. An electrode of this type has a very good cutting capacity even in the case of tall workpieces. A disadvantage, however, is that such an electrode is relatively cost-intensive to produce. In this case, on the one hand, an accurate alloy composition of the core must be maintained and, on the other hand, diffusion has to be carried out over a long period of time at high temperature in order to achieve a state of equilibrium. This state subsequently has to be fixed by rapid cooling. It is extremely difficult here, in this known process, to control the phase fractions in the sheath layer accurately. Slight deviations in the production process lead to the presence also of alpha and/or gamma brass in the sheath layer in addition to the beta brass.